Electric cooking device



March Ll-7 I, R H, PARK 2,233,485

ELECTRIC COOKING DEVICE Filed sept; 29, 1953 4 sheets-sheet 1 ELECTRIC COOKING Dlsvc:

Filed Sept. 29, 1938 4 Sheets-Sheet 2 March 4, 1941. R, H, PARK LEcTRrc COOKING DEVICE Filed sept. 29, .195e 4 sheets-sheen 5 March 4, 1941. R. H. PARK ELECTRIC COOKING DEVICE Filed Sept. 29, 1938 4 Sheets-Sheet 4 Pawn?,

Patented Mar..4, 1941 UNITED vSTATES PATENT OFFICE 2.23am Enfermo oooxnvo nevrosi ueber: u. Pm, ripckemin., er. J. application september ze, ross, serian No. ceases 14 claims. (ol. 21e-43) This invention relates to electric cooking and the object is to provide an improved cooking vessel having a self-contained heating element and coordinately therewith improvements both g' in the mechanical and electrical construction of the "stove" with which it is used.

My invention will be Well understood by reference to the following description ot the illustrative embodiment thereof shown by way of example in the accompanying drawings,- where- Fig. 1 is a vertical transverse section of a saucepan constructed in accordance with my invention positioned on the top oi a stove, only a portion of the latter being shown;

Figs. 2 and 3 are sections on the lines 2-2 and 3 3 of Fig. 1 respectively;

Fig. 4 is a wiring diagram of the heating elements incorporated in the cooking vessel; 2d Fig. 5 is a fragmentary section on a greatly enlarged scale showing the connection to 6the heating elements proper;

Fig. 6 is a fragmentary enlarged section illustrating the connection to the vessel oi' the ter- .25t minal studs by means of which the heating elements are connected to a source of current;

Fig. 7 is a horizontal section on the line 1 1 of Fig. l; and

Fig. 8 is a Wiring diagram.

As contrasted with the customary electric cooking apparatus wherein heat is radiated .from a resistance element to the vessel containing material to be cooked, a method inefficient for boil- Gli ing or like operations, the apparatus which I 35 am about to describe makes use of a vessel having a self-contained heating element in cihcient thermal conducting relation to the wall of the vessel and 'adapted efficiently to supply heat by conduction to the contents thereof.

40 Many features of construction herein disclosed are substantially like those shown in my prior Patents 012,618 and 2,045,673 and therefore will require only hrief description herein. En contrast with the specific disclosures of those 5 patents, the cooking apparatus herein shown is adapted to be operated directly from the ordinary llii volt current-supply lines usually found in residences without the use oil step-down transformer. l

5u 'i' have herein shown a cooking vessel 9 of the saucepan type having projecting downwardly from its bottom terminal studs il through which current is supplied to the heating elements hereinaiter more fully to he described,l which studs s are adapted to enter between and he grasped by not in use.

pairs of Jaws I1 through which the current is supplied.v As indicated by the partial illustration in Figs. 2 and 8, these jaws may be mechanicaliy operated and electrically governed as in my aforesaid Patentl 2,945,673, to which -ref- 5 erence is made for a fuller illustration, each pair being herein plvoted together on a pivot 23 and having a normally open position to permit the introduction of the studs Il between the same, and they are adapted to be swung to clamping i@ position against the studs by the operation of a. reversible electric motor t5, the arrangementv being such that the Jaws are completely closed before current is supplied thereto and conversely current is cut off before the jaws open. Without repeating in extenso the description given in the prior patent referred to, control of the cooking operation is effected by means of the hand-operated switch 1i (Fig. 8) of the double-pole, double-throw type shown in the oif position in that figure wherein all the parts are in the position they would assume when the stove was The pan is placed in position 'by a simple movement oi superposition with the studs I i extending between the open jaws, and when A the switch Il is thrown, motor is energized which results in the mechanical closing of the switch B5, a mechanical advance of the clampingl jaws to closed position by turning of the shaft 3i which has right and left threads engaging 39 respectively the jaws of a pair, and ultimately a movement of switch which oath breaks the motor energizing circuit and also closes the circuit of solenoid Si, lifting bridge QS and causing current to flow to the clamps. After the cook- 35' ing is completed, when the main switch li is shifted back to the position shown in the drawings, the movement of bridge of the switch breaks the circuit of solenoid coi El and thus opens the heating circuit. Further it reenero gizes the motorv to cause its rotation in the reverse direction which in turn first provides for return oi switch B5 to the position iliustrated under the action of spring h3 and then cause s rotation oi' shaft El in a direction to open the clamps.

LThe heating current is supplied tiirough conductor 98 and under control of the seiector switch 91 governing the auto-transformer 2i through 50! wire it to the left-hand stud il illustrated in Fig. 8 and from theA right-hand stud leads. through the coil i i3, hereinafter to he referred to, and through the bridge S5 and wire 95 to the ,opposite side of the line. The voitage applied and the intensity of the heat are regulated by manipulation of the switch 91.

Further to describe the electrical features illustratedin Fig. 8, I have there shown a safety mechanism substantially similar to that shown in my Patent 2,070,491 responsive to a change in the impedance of the cooking vessel, herein effected in a manner hereinafter more fully to be described, to interrupt the circuit when the vessel cooks dry and thus prevent objectionable burning on of semi-liquid matter or destruction 4of the vessel by melting. This mechanism comprises a switch in the circuit of solenoid 9| having a fixed contact 99 with'which cooperates a spring blade IOI carried by a rocking beam |05 normally held closed by a spring |09. Opposite ends of the beam are here shown as connected to the coils H3 and II5 respectively. The coil III is arranged in series in the heating circuit as already described and is so wound as to attract its core with a force which is a function of the current (amperage). CoiliI5 is of high resistance and may be bridged across the studs II, conveniently with the addition of a resistor II'I, and acts on its core with a force which is a function of the electro-motive force or voltage. When the impedance of the pan circuit substantially changes (increases .in this particular instance), the force of coil II5 overcomes the force of coil IIB, rocking beam |05 clockwise, opening the circuit of solenoidl, which in turn shifts bridge 95 from its contacts and opens the heating circuit, which'remains open until the switch is manually -reclosed.

To provide a cooking vlessel having an inbuilt heating element adapted to operate on ordinary house current while providing a mechanical construction of adequate simplicity and suilicient lightness of weight, I utilize by means of the novel features of construction hereinafter described resistance elements of nickel-chromium` ,alloy commonly known commercially as Nichrome. Suchmaterial has a low temperature coefficient. To permit the effective operation of the safety control just described, therefore, I preferably utilize (see Fig. 4) two heating elements I2 and I2a arranged in parallel, one being under control of a thermostat I4, which may be of the snappingdisc type described in principle in United States Patents 1,448,240 and 1,718,716 and unnecessary to illustrate in detail. Commercial forms of such thermostats are well known on the market. If the pan boils dry and begins to heat unduly, the thermostat operates to cut element I2a out of the circuit, thereby markedly increasing the impedance of the vessel and causing the operation of the switch at 99-IOI.

The arrangement just described is particularly advantageous since the operation oI.' the safety device depends only on temperature substantially independently of the rate of heat application. Due to the ylow temperature coefiicient of the resistance elements employed, their resistance does not substantially vary with rate of heat application. If, on the contrary, there were a tendency for an increase in resistance with rate of heat application, it would be necessary to set the safety device for a relatively high value of resistance which would mean that at low rates of heat input (low applied voltage) it would not operate until a relatively high pan temperature has been attained. This diiliculty is avoided with the arrangement shown.

Referring now to the mechanical features of construction of the vessel 9 illustrated, I have herein shown itas comprising a cup-like body having an inner bottom I6 which supports the contents of the same and an outer bottom Il defining with the inner bottom a water-tight intervening chamber and from which outer bottom project downwardly the terminal studs II. A depending marginal flange 20 permits the vessel to be set on a horizontal surface without interference from the studs II.

The resistance elements proper I2 and I2a may be of more or less conventional construction consisting of a suitable wire wound on a sheet of mica and located between two mica sheets, and I have considered it unnecessary to illustrate these in detail. To provide for efficient thermal contact of these resistance elements with the bottom I6 of the pan without bulky or unduly heavy parts, I may provide the grooves 22 and 24 in the under side of the bottom of the pan, these grooves preferably being of annular form which, besides providing for good thermal distribution, permits them to be simply cut by a suitable tool in a single rotary cut. Ihe resist ance elements I2 and I2a are of like annular form and are received in these grooves and firmly pressed against the bottom 'IB by means of annular pressure plates 26 and 28 respectively, which f it in the grooves and are securely and firmly held by upsetting the material of the bottom at the sides of the groove over the margins of these plates, as clearly illustrated in Fig. 1. Because of the annular construction, these plates are of relatively restricted width, providing for a uniform pressure onl the overlying resistance elements. I have herein shown the inner pressure plate 2B as provided with a depending` a head received in a recess 36 therein. The end of the resistance element I2 may extend through a hole in the head and be interposed between the lower face of this head and a washer 38 surrounding the shank. Conductor 40 is received between washers 42 at the outer end of the shank, suitableiinsulating washers 44 being provided to insulate the washers 38 and 42 from the pressure plate 26, and the upsetting of the shank of the stud on washers 42 binds all the elements firmly together. The conductors 40 lead through the chamber between the bottoms (Fig. 3) to connecting arms 46 carried on the studs II.

The method of mounting and connecting the studs II will be best understood from Fig. 6. It will be understood that in a device for this purpose a smooth exterior surface is desired ca.- pable of being kept clean and that the connection must -be air-tight and capable of considerable abuse. The( construction which I am about to describe is as a matter of fact capable of withstanding a sdewise thrust on the studs II of at least one hundred pounds. As seen in Fig. 6, the relatively thin lower bottom I8 of the vessel is provided with apertures of relatively great size as compared with the diameter of the studs, which apertures have extending upwardly therefrom deep flanges HI. Received and supported .the corresponding homologous portions of the by these flanges are massive blocks 59 of suitable studs so that, se illustrated in Fig. .7, While the insulating materiel Whieh may be a compound of lett-hand stud may make contact with the leftmloe and loorex, commonly known commercially hand opening 62 at the three oclock position,

e es Micelex. Preferably I make these blocks there is a, clearance between the corresponding ,5 slightly larger than the opening in which they pointe o! the right-hand stud end opening so me to be eeeeived end shrink the o'nges 48 that no short ciecuit through the cover plate Sii thee'eeeout to meute e positive t which will eptle. not yloosen when pen. is`heeteo. The studs Preferablys ee best seen in Figs. 2 and 1, the

21e M efe carried ey these blocks E@ and they are etude M have flanges et their lower enfle -providw herein showt ae provided with reduced Shanks ing abrupt, upwardly feclng shoulders and the denimg ehoialdeee which seat on the loweil engaging portions o the jaws, which have cori'eezcee of the blocm Hush with the bottom I8 of spending dowmwotdly meine, eorupt :shoulders the pen.. shane-s extending through the 551, eleep the vexticei sides of the studs alcove Ee moeite he tifeteei eveiweshei'e 5&3, drawing these emi oveziie 'the some to provide e 5&5 so Weteiftigiit engagement with positive mtelocr; against Withdrawal of the .studs bloote. The c meting erm te ie seemed in from bett-veen the elceed Saws. "if it le ettempted joint eetin'eee the Washer and the meek, Y to remove the vessel Wit-hout opening the jews, telve meule ing miette? 5 of mice oin time like ,no Beoefening eteeee io plowed upon the letter since fe eege-elfeting :it no. the impe? end of the iienge eiouldete GG 8@ engoge in e lievemente! 2 it, Westiee 36 overhang the ezoele of flanges pleine i353 :me 'tnei'eoee unete? excess neet (es when E ewoee that e invention meer be em heile eey? the shrink joint o these bodied in siteA me Without departing n loosen, the ts'focke cannot feti. out fiom. the spint or .fe ettl'iiutee the i @inizi tightness. oi"- the joint will be and "I therefore desire e yeieeeitt emoo to "oe cenefldei'ed in respecte illustrative met eestietive; reference nod leemte@ @Reime mtime' hem te v- "i to imiioote me ecefe of the inventior liepen is e. cove, for have or i eed *mi l. eooking vessel 'limitn ii'ieomoxeted weil thereof e. hee Ieiez @emp atei? ecoeseioly eiloesec my auch except oi o" teeiiimele projeetiig ilioin s metI ezwoeea Y kof smell pioeotloite. the exterior of the veeee i'lsee e, veertien Meeting; element im en ete-w ne oir;

I in@ eeioent comprime@ mee elements one etuee M, the

e 3eme no', el@ v olif which is). e 1

ie teething; to e t 'cl the plete lede -e'- tn e, effettive ei" tizio vessel WeB adje mcreosee above determined velue, e the Vessel boils dry, means fo? connect ng `e ttoioege seid terminale to e. somme of and t J eleettio means fot' eonti'oling in substan- *oii exijo;7 hete tine tiel degree the voltige supplied to the circuit no; eennot whereby to contiol the rete of heet supply to the y plete to Vestel, switch comtt'otlmg supply of enemy te mote. Thur-5, wier@ dieremtielly ectine; memes conzi the reepeotive melee ti'ol'iinfg .seid switch compri-teilig en electrmmegetude imm opposite netie motie- 'device responsive to the voltee'e enel eeeto-mognetiemotoe device in e diieremt Y@ megeetic cicut esponsive to the current wheieertiene oy to open .switch om cionormel increase of .e ocloc position mieeeiice im the vessel. spolceol in e.. eireetion in en eiectic cooking device in combination the ine im e distance fgieetein than with e. cooking vessel heaving' within e well there- 75.

of an electrical heating element comprising a pair of parallel resistance elements in thermal contact with but electrically insulated from said wall and having terminals exposed at the exterior of the vessel vfor including the heating 'element in an electric circuit, the heating element comprising a temperature responsive means adapted to cut out one only of the resistance elements when the temperature. of the vessel wall adjacent thereto increases above a determined value, as when the vessel boils dry, means for connecting ,the same in an electric circuit to a source of electrical energy, the said circuit exterior of the vessel comprising a manual control switch and an electrically operated switch responsive to such change of vessel impedance to open the circuit.

4. In an electric cooking device in combination with a cooking vessel having within a wall thereof an electrical heating element in thermal contact but electrically insulated therefrom having terminals exposed at the exterior of the vessel for including the same in an electric circuit, the element embodying means effective temporarily substantially to change the impedance thereof when the temperaturel of the vessel wall adjacent thereto increases above a determined value, as when the vessel boils dry, means for connecting the same in an electric circuit to a source of electrical energy. the said circuit exterior of the vessel comprising a manual control switch and an electrically operated switch responsive to such change of vessel impedance to -open the circuit.

5. An electric cooking vessel having a self-contained heating element and having a bottom exteriorly uniform to V.permit the effective wiping traverse of a cleaning cloth or the like over the same, said bottom having openings therethrough bounded by inwardly extending flanges, massive blocks of insulating material fitted within the flanges and terminating substantially flush with said bottom, the flanges being normally stressed in tight gripping relation to the blocks to retain the latter as such and to provide an impervious Joint, and imperforate terminal studs for the heating element having impermeable connection with and supported by the blocks in spaced relation to the flanges and projecting below the bottom.

6. An electric cooking vessel having a self-contained heating element and having a bottom exteriorly uniform to permit the effective wiping traverse of a cleaning cloth or the like over the same, said bottomhaving openings therethrough .bounded by inwardly extending flanges, massive blocks of insulating material fitted within the flanges and terminating substantially flush with said bottom, the flanges being normally stressed in tight gripping relation to the blocks to retain the latter as such and to provide an impervious Joint, and imperforate terminal studs for the heating element projecting below the bottom having shouldersv resting on the blocks and integral shanks extending through the same, the

Ishoulders making an impermeable joint with the lower faces of the blocks and the Shanks supporting the studs in spaced relation to the flanges.

'1. vAn electric cooking vessel having a self-contained heating element and having a bottom exterioriy uniform to permit the effective wiping traverse of a cleaning cloth r `thelike over the same, said bottom having openings therethrough bounded by inwardly extending flanges, massive blocks of insulating material fitted within the flanges and terminating' substantially flush with said bottom, the flanges being normally stressed in tight gripping relation to the blocks to retain the latter as such and to provide an impervious joint, washers opposing the inner ends of the flanges, and terminal studs for the heating element projecting below the bottom of the vessel having shoulders pressed against the lower faces of the blocks in spaced relation to the flanges to form an impermeable joint and shanks extending through the blocks and engaged with said washers.

8. An. electric cooking vessel having a double bottom, the inner bottom, which in use supports the contents of the vessel, having a resistance element supported in firm thermal conducting contact with the underside thereof, the outer bottom being exteriorly uniform to permit the effective wiping traverse of a cleaning cloth or the like over the same and having openings therethrough bounded by inwardly extending flanges, massive blocks of insulating material fitted within the flanges and terminating substantially flush with said bottom, the flanges being normally stressed in tight gripping relation to the blocks to retain the latter as such and to provide an im* pervious joint, solid terminal studs for the heating element having impermeable conhection with and supported by the blocks in spaced relation to the flanges and projecting below the bottom, and connections between said studs and element received between the bottoms.

9. An electric cooking vessel having a double bottom, the inner bottom, which in use supports the contents of the vessel, having a resistance element supported in firm thermal conducting contact with the underside thereof, the outer bottom being exteriorly uniform to permit the effective wipingtraverse of a cleaning cloth or the like over the same and having openings therethrough, massive blocks of insulating material carried by the outer bottom and providing "an impervious closure for said openings substantially flush with said bottom, solid terminal studs for the heating element having impermeable connection with and mounted in said blocks in spaced relation to the margins of the opening, said studs projecting below the outer bottom, and connections between said studs and element received between the bottoms.

10. Electric cooking equipment, in combination with a vessel having a self-contained heating element and terminal studs therefor projecting downward below the bottom of the vessel, a current supplying system having pairs of jaws between which the studs are received, a support for receiving the bottom of the vessel having openings through which the studs may project vertically to be lengaged by said jaws, the size and location of the openings in a horizontal plane being such that in any position wherein the studs are s0 engaged only one thereof may be in contact with the support at the margins of the openings.

11. Electric cooking equipment, in combination with a vessel having a self-contained heating element and terminal studs therefor projecting downward below the bottom of the vessel, a current. supplying system having pairs of jaws between which the studs are received and adapted to close thereon from opposite sides of a line connecting the studs, a support for receiving the bottom of the vessel having openings through which the studs may project vertically downward to be engaged by the jaws, the distance measured parallel to -said line between homologous portions of the margins of the opening being greater than the distance between homologous portions of the studs whereby the studs cannot simultaneously contact margins of the openings on displacement of the vessel along said line.

12. In electric cooking equipment, in combination, a vessel having a self-contained heating element and terminal studs therefor depending from the bottom of the vessel, a current supplying system having pairs of relatively movable jaws having an open position permitting the studs to be freely placed between the jaws with clearance therefrom and a closed position grasping the studs, means for operating the Jaws, an insulated coverplate overlying the jaws and having openings oi substantially greater size than the studs through which they maybe inserted and the margins o! which are located to guide the studs between the opened Jaws, said margins being differentially positioned relatively to the peripher ies of the studs to exclude simultaneous contact or the studs therewith when the jaws are closed.

13. In electric cooking equipment in combination with a vessel having a self-contained heating element, depending supporting means adjacent the periphery thereof o'n which the vessel may stand, and terminal studs depending from the bottom oi the vessel within the ambit of the supporting means, a current supplying system having a smooth top on which the supporting means may rest and a relatively small insulated cover plate to project upwardly within the ambit or the same having openings therethrough through which the studs may loosely extend, and pairs of Jaws connected respectively to opposite sides of a source o! current located beneath the openings and having an open position permitting the studs as guided by margins oi said openings to be freely entered between the same with clearance therefrom' and a closed position grasping the studs.

14. In electric cooking equipment, in combina tion, a vessel having a self-contained heating element. terminal studs depending from the bottom thereof hav nanges de abrupt, upwardly 'facing shoulders. a current supplying system having pairs of relatively movable Jaws having an open position permitting the studs to be freely placed between the Jaws with clearance therefrom and a closed position wherein engaging portions of the jaws overlie the flanges to provide a positive interlock against withdrawal oi the studs and clasp the studs above the ilanges and means for operating the jaws.

ROBERT H. PARK. 

